Urinary tract infection (UTI) is a major medical problem confronting people who have spinal cord injuries (SCI). SCI patients, especially those with indwelling catheters, are usually colonized. These resident bacteria may or may not cause symptoms. Those that do not are frequently considered benign colonizers and are often left untreated because they may afford some protection against superinfection with more harmful bacteria. Usually, little is known about the asymptomatic colonizer, especially in regard to its capacity to "protect" the host or its ability or inability to cause symptoms at a later time. The concept described herein of using a benign bacteria to prevent infection by a more virulent one is called bacterial interference. In this project we propose to test the usefulness of bacterial interference for prevention of symptomatic UTI in SCI patients who have a him% of recurrent symptomatic UTI. We will use a benign colonizing bacteria, a well studied Escherichia coli strain, which has previously been shown to colonize bladders of people with neurogenic bladders. This strain, designated E. coli 83972, lacks several properties deemed requisite for a bacteria to cause systemic UTI. Indeed, these bacteria did not cause systemic illness in any of 17 previously successful bladder colonization attempts. Colonized patients instead reported subjective improvement in medical status. Based on this experience, we postulate that bladder colonization by E. coli 83972 will reduce the frequency of UTI in patients with SCI. In addition to bacterial and clinical studies, the immune status of our patient group will be monitored. The purpose is to measure the contribution of patients' immunity to the success of bacterial colonization as a treatment for preventing UTI. Additionally, selected patients with maintained asymptomatic bacteriuria will have their organisms studied, if E. coli, as to why they may provide protective properties.